In recent years, it has become known that articles having an uneven microstructure on a surface thereof with a period not more than the wavelength of visible light exhibit an antireflection effect, a lotus effect, and the like. Particularly, it is known that an uneven structure that is constructed with approximately convex cone structures, a so-called moth-eye-structure, becomes effective antireflection means since the refractive indices keep increasing continuously from the refractive index of the air to the refractive index of the article.
As a method for forming an uneven microstructure on a surface of an article, the following method arouses interest: an active energy ray curable resin composition is interposed between a mold having an uneven microstructure on a surface thereof and a substrate and cured by the irradiation with active energy rays to form a cured resin layer having the uneven microstructure transferred thereto on a surface of the substrate.
Furthermore, as the mold, a mold having an anodized alumina oxide with plural pores on a surface of an aluminum-based substrate attracts interest, from the viewpoint that the mold can be simply prepared (Patent Literature 1).
However, the mold has a problem that the contact interface between the mold and the active energy ray curable resin composition increases drastically for the following reasons (i) to (iii), and therefore, it is difficult to release the mold from the cured resin layer.
(i) The average interval of the pores in the anodized alumina oxide is from about 100 nm to 400 nm, and the distance between the pores in a portion having pores closest to each other is from a few nanometers to a few tens of nanometers. That is, the structure is very fine.
(ii) As described in Patent Literature 1, in a case where the pores are formed by performing anodization and etching repeatedly, the smoothness of the wall surface of the pores may decrease, and thus, the wall surface of the pores may become coarse to some degree in some cases.
(iii) In a case where it is intended to obtain a function such as a sufficient antireflective effect, it is necessary to adjust the aspect ratio of a pore to a relatively large value.
Examples of the mold for improving the releasability of the mold from the cured resin layer include a method in which the surface on the side where the uneven microstructure of the mold is formed is treated with a release agent (mold release agent) that reacts with the surface of the mold (Patent Literature 2).
However, the method has the following problems (iv) to (viii).
(iv) In a case where the uneven microstructure of the mold is transferred repeatedly, the mold release agent is detached from the surface of the mold, whereby the releasability is gradually reduced. If the releasability is reduced, the productivity of the article is also reduced, and a part of the transferred uneven microstructure is damaged, and the transfer accuracy is thus also reduced.
(v) There are some cases where the mold release agent detached from the surface of the mold moves to the surface of the article, which is thus fouled, and therefore, as the number of times of transfer increase from an initial time of the transfer, a remarkable change in the characteristics of the surface of the article is actualized. Further, in a situation where the mold release agent is detached, the height of the convex portions of the transferred uneven microstructure is gradually changed, and consequently, the surface physical properties as well as the optical characteristics of the article are also changed. As a result, after the initiation of the preparation, an article having an uneven microstructure on a surface thereof obtained during the change in the characteristics of the surface and the optical characteristics cannot be shipped as a product, resulting in a waste of the raw materials and the source materials consumed until the surface of the article characteristics and the optical characteristics are stabilized.
(vi) In a case where the fluorine-containing silane compound and the fluorine-based solvent, each described in Patent Literature 2, are used to subject a mold to a release treatment, the cost required for the release treatment with an increase in the area of the mold poses a problem from the viewpoint that the fluorine-containing silane compound and the fluorine-based solvent are expensive. In particular, it is expected that such a problem becomes apparent in a case where the mold has a roll shape and the whole roll having a large size is immersed in a treatment liquid.
(vii) The fluorine-containing silane compound has a problem in a stable and uniform treatment of the surface of the mold since aggregates due to the reaction between the silanol groups in a case of absorbing moisture are generated. As a result, there are some cases where when the liquid accumulation of the release treatment liquid is generated when the release treatment is carried out, the aggregates of the fluorine-containing silane compound remain in the portions with the liquid accumulation, which become the defects of the mold.
(viii) In a case where unwanted residues and the like remaining on the monomolecular film of the fluorine-containing silane compound formed on the surface of the mold are rinsed with a fluorine-based solvent, the number and the cost of the steps further increase.